There are many applications requiring the storage and handling of disc-shaped objects (hereinafter referred to as "discs") allowing contact only on their edges. One example of this would be in a library for storing optical discs, audio compact discs, photo compact discs, etc. Other kinds of discs that may only be touched at the edges that may be suitable for robotic handling include silicon wafers in an integrated circuit fabrication facility, lenses, mirrors, optical filters or other optics in a fabrication, coating or assembly facility, etc.
For example, in U.S. Pat. No. 5,107,475, an automatic disc changer is disclosed in which tray guides are provided on a large number of levels in a case at right and left portions thereof so that the center line of the guide on each of the levels of the right portion and that of the guide on the level of the left portion extend toward a tray transfer mechanism and meet each other in the form of a V. The tray transfer mechanism can be moved up and down between each of the guides and a disc player for playing a disc in a tray transferred by the tray transfer mechanism, be swung from a central portion to positions corresponding to the guides on each of the levels at the right and left portions, and be moved backward and forward, to and from each of the guides.
Furthermore, in most libraries, separate disc transfer and support members are used to store and retrieve discs. Such members do not utilize the round shape of the discs in moving them between the storage slots and drives. This requires extra parts to be contained in the carriers or cassettes for each disc, complex mechanisms for sliding the disc carriers without jamming, and the need to have a mechanism to separate the carrier from the disc or open a shutter. Hence, to spin the disc, the disc must be separated from the carrier or a shutter on the cassette must be opened. Also, these mechanisms not only creates debris associated with sliding the separate transfer and support members, but also the carriers or cassettes often wear out.